Infusion machines and units for infusion preparation are known in the art. In particular machines are known, for instance vertical type superautomatic machines, that comprise devices for the ejection of already exhausted infusion powders.
For instance, a device for the ejection of already exhausted ground coffee and applied to a coffee preparation vertical machine is known from Publication EP—0528758.
The known machine comprises two opposed pistons, an upper piston that is stationary and a lower one, a cylinder associated to the lower piston and apt to form a chamber with it, and an ejection arm having a first end pivoted to the cylinder.
During the infusion step, the cylinder, guided by a rotary shaft having a rotary axis outside of the cylinder, pulls the lower piston in the direction of the stationary piston so as to realise an infusion chamber formed by the stationary piston, the cylinder and the lower piston.After the tamping of the ground coffee and the corresponding infusion by means of water flow in pressure, the cylinder is guided in a direction opposite to the stationary piston by pulling the lower piston itself with it and holding the ejection arm in a rest position.The movement of the lower piston ends before that of the cylinder due to suitable stops fastened to the frame, therefore the cylinder continues its movement until the lower piston head, which has a convex shape, emerges from the cylinder, having convex edges too, so as to align the lower piston head to the cylinder edges and to cause emersion of the exhausted powder.At the end of the movement, the rigid type ejection arm, which has a spatula of concave shape at a second end, is activated and set into an arc motion (pendulum type motion) around a pivot so as to eject the exhausted powder that is on the piston convex head.In particular, the ejection arm comprises a lever that protrudes from the pivot wherein the first end is pivoted so that a first protruding element, fixed to the base of the frame, at the end of the cylinder movement, is capable to activate the rotation of the lever and of the ejection arm connected to it.In a next step when the cylinder goes up, the lever runs into a second protruding element, fixed to a side of the frame, arranged to force a rotation in the opposed direction of the lever and of the arm so as to restore the rest position of the ejection arm.
A first problem of such a prior art is that the ejection mechanism comprises elements associated to the cylinder: the arm, the pivot and the lever; elements associated to the base of the frame: a first protruding element; elements associated to the sides of the frame: a second protruding element; all elements that, being associated to various parts of the machine, make complex a calibration of the device that might be necessary, for instance, due to the wear and tear of protruding elements and/or of the lever that co-operates with protruding elements and/or of the spatula.
Such a problem, obviously, is worsened by the fact that the area wherein the lever and the protruding elements work typically comprises ground coffee mixed with water which is, as known, strongly abrasive.
A further problem of such a prior art is that it requires to shape the piston with a convex head and the cylinder, analogously, with convex edges, in order to avoid that exhausted ground coffee is accumulated on the piston head and/or on the cylinder edges.
Obviously, as is easily comprehensible to a technician in the field, a curved shape of the piston head is not optimal for obtaining a uniformly distributed pressure on the infusion powder and therefore for obtaining a good infusion.
A further more general problem of such a type of prior art is related to the fact that the cylinder and piston movement is operated by means of devices being not in axis thereto so that the acting forces typically are not balanced and this causes wear and tear of the moving parts, similarly not balanced.
Other publications related to vertical machines are also known wherein a mechanical device is provided for the exhausted powder ejection.
For instance from Publication EP—0298544 an infusion machine is known wherein an ejection device is provided whose movement, a pendulum type movement, is associated to a corresponding movement of one of the pistons.
A further example is described in Publication EP—0756843 wherein the ejection device performs a movement transversely to that of the pistons and requires the support of a plurality of mechanical cams and leverages in order to synchronise the movement of the device to that of the pistons.Still another example is known from publication EP—0299399 disclosing a vertical machine configured for ejecting the exhausted powder by means of warm water.Such types of solutions seem particularly far from the solution provided according to present invention.The Applicant points out that all the known solutions either are particularly complex and of difficult calibration, or are ineffective as they do not ensure a perfect removal of the exhausted powder.